The present invention concerns a device and method for forming welds, particularly wax welds, to couple individual pattern segments together during assembly of casting patterns.
Investment casting is a process for forming articles from metals and alloys. Casting molds are created for receiving liquid metal or alloy during the casting process. To make a casting mold, casting patterns are formed in a shape of the desired article from a wax or polymeric material. A refractory shell is formed about the pattern by serially dipping the pattern into aqueous or organic suspensions comprising refractory and other slurry materials, thereby forming an investment casting mold.
For complex shapes, plural pattern segments made from wax or polymeric material must be joined together by welds. Historically, seams between pattern segments have been formed by skilled operators using techniques such as single and double tape wax-weld-forming methods. Two or more pattern segments are first placed upon an assembly fixture, such as a table which can be rotated in various directions. Tape is applied to the exterior surfaces of two adjacent pattern segments and across a seam region defined by adjacent pattern segment edges. The tape forms a barrier for receiving or retaining wax in the seam region, and may be placed on one side or both sides of the adjacent pattern segments (i.e., single or double-tape methods). An operator rotates the fixture into a position suitable for feeding liquid wax into the seam region between the two segments. Placing the wax properly between the two pattern segments and in the seam region can require rotating the fixture, and therefore the pattern segments attached thereto, in various directions. Rotating the fixture allows the wax to flow uniformly through the seam, and further may facilitate expelling any air that may form bubbles in the wax. Once the junction between pattern segments is filled substantially with liquid wax, the wax is allowed to solidify to form a wax weld. An operator inspects the weld to make sure it is flush with the walls of the pattern segments and for any other defects.
The conventional weld-forming process is time consuming, often requiring 8-40 hours to form welds between segments, and labor intensive. A need therefore exists for a method for forming welds between adjacent pattern segments.
The present invention provides an apparatus and method for forming welds between adjacent pattern segments used to assemble monolithic casting patterns. The described embodiments generally eliminate the need to rotate fixtures and substantially reduce the time required to form welds.
One embodiment of a disclosed seam tool comprises a rigid backing configured to be positioned about a seam region defined by at least two adjacent pattern segments. The rigid backing further includes an injection port and, typically, a gas outlet port, fluidly coupled to the seam region. The disclosed device may further include a resilient liner on a surface of the rigid backing, which resilient material contacts and forms a seal with surfaces of the pattern segments. Compensating grooves may be formed in the resilient material to allow complete filling of the seam region by weld-forming material.
An additional disclosed embodiment of a seam forming tool comprises pattern segment clamping means. The clamping means include an injection port for receiving weld-forming material and, typically, an outlet port, fluidly coupled to the seam region. The device also typically includes seal means, such as may be formed from a resilient material, with or without a compensating groove. Another disclosed embodiment includes an injection fitting operably coupled to an injection port.
A method for forming a weld between plural, adjacently positioned pattern segments also is disclosed. The method comprises positioning the disclosed embodiments of the seam tool about a seam region defined between adjacent pattern segments. A weld-forming material is introduced into an injection port fluidly coupled to the seam region, and allowed to solidify to form a weld in the seam region.